Bob wrote in
:

The Sangean external antenna input is a 2.1mm jack which would
acommodate a high impedance long wire, as per the instructions:


3.5mm, not 2.1mm

"ANT-60 PORTABLE SW ANTENNA
Included with the ATS-909 is the Sangean ANT-60 Portable SW Antenna.
The antenna is plugged into
jack (26) labeled EXT AM ANT. When fully extended this antenna should
improve SW reception. For
maximum performance this antenna should be placed as high as possible
above the ground and in an
unobstructed area if possible."


I know that, it was the first thing I found, but it doesn't answer any
questions about impedance, especially if the radio you buy is second hand and
doesn't have the antenna wire with it.

Your idea of attaching the antenna via 50 ohm coax would probably be
below the impedance range of the jack, tho' I'm not sure you would
really hear much difference.

If the Sangean external antenna input were designed for 50 ohm coax,
it would probably have a coax jack, not the 2.1 mm jack.


Agreed, which is why I don't assume it's 50 ohms, and I start looking for
answers. I think you're likely right that it might not make enough difference
to worry about though. If using coax can get the SNR higher I'm in business
so long as the signal is strong enough for the input's gain to use.